• Summary
• Introduction
• Factors in determining the starting dose
• The dangers of prescribing too much/not enough
• How much methadone should you prescribe?
• Methadone equivalent doses
• Dose titration

Summary

• Methadone is a potentially lethal drug.

• Prescribers should avoid allowing patients to take away initial doses of methadone sufficient to cause accidental overdose i.e. 50mg or less, if there is concurrent benzodiazepine or alcohol use.

• If you are in the position of having to make a decision about prescribing and you have any doubt in your mind, it is better to be safe than sorry. Refer to a specialist drugs service or doctor with experience for a second opinion.

• Ask your local drugs agency to help you fill in the equivalent dose ranges for the illicit heroin to methadone chart.

• Always titrate the dose against prevention of withdrawal symptoms and reduction in cravings for illicit opiates rather than against the observable intoxication.

• Start off with the lowest workable dose based on a thorough assessment and increase if necessary.

Introduction
Having decided to commence methadone treatment, calculation of the correct starting dose when commencing treatment is a difficult and contentious issue. This section is mainly intended to give guidance to the non-specialist prescriber as to the principles governing calculation of the appropriate methadone dose.

Before methadone treatment can commence there must be a full and thorough assessment and clear treatment aims must be defined.

The decision as to how much methadone a person should be prescribed is not simply a calculation of the equivalent dose of methadone to the amount of opiates they are taking.

For these reasons this section must not be read in isolation but in the context of the rest of the book, particularly:

• Section 2: The research basis for methadone prescribing
• Section 6: Assessment
• Section 7: Treatment aims and choices.

Factors in determining the starting dose
The calculation of the 'right dose' must take into account the following factors:

• The 'right dose' varies according to the treatment aim
• Illicit heroin varies in purity from area to area and from time to time
• Clients may exaggerate their drug usage to obtain more methadone
• Workers may underestimate clients' drug use to reduce the amount of methadone they prescribe
• Methadone is a long-acting opiate
• Too much methadone can be fatal or lead to illicit sale but insufficient methadone is unlikely to be effective.

These factors are dealt with in more detail below.

Treatment aims
The optimum amount of methadone for each person will vary within a given range according to the amount of opiates they are taking and the agreed treatment aims. If the chosen treatment option is detox then the aim will be to determine the minimum daily dose of methadone that will keep the client free of withdrawal symptoms.

If the client is an intravenous user and the treatment aim is to use methadone to help them stop injecting, by giving them enough to greatly reduce the desire to use heroin, then they will probably need more methadone than someone who was smoking the same quantity of heroin per day.

Variations in heroin purity
Variations in heroin from area to area tend, on the whole, to remain fairly constant - purity levels in London would typically be consistently higher than purity levels in the provinces.

Batch to batch purity can change - generally with a given area experiencing a week or so of supplies of 'bad' heroin i.e. below average purity, every now and then, or, conversely, a week or two of 'good' heroin i.e. above average purity.

However, on the whole, agencies who do a lot of prescribing within a given locality retain a fairly constant baseline conversion level of heroin to methadone for people who want to detox.

Exaggeration of drug usage by clients
As the accurate determination of actual drug usage and tolerance are essential components of any prescribing assessment this issue is discussed in detail in Section 6: Assessment.

Deliberate underestimation of drug use
Many drug services have ceilings (both official and unofficial) as to the amount of methadone they will prescribe. In such cases it can be tempting to disbelieve a client's estimation of their drug use in order to justify prescribing a sub therapeutic dose. However it is better for both client and worker for prescribing ceilings (where they exist) to be made explicit in the assessment process, and to directly address any difficulties this may cause.

Methadone is a long-acting drug
Methadone's long action can cause problems: (see Section 4: Physiology and pharmacology of methadone)

• Methadone feels different to heroin
• The slow onset of action is markedly different from heroin
• Methadone builds up in the system over the first 3 days.

Methadone feels different to heroin
Clients often expect (or hope) that, as a heroin substitute, methadone will make them feel similar. Lack of understanding of this phenomenon is often a feature of high-dose requests from clients who come for their first methadone prescription. In the past they may have taken large quantities of illicit methadone on a one-off basis and found that they did not experience the usual opiate euphoria. They often conclude from this experience that they need much more than they had before in order to replace the heroin they are using. When it doesn't, they often believe a higher dose will achieve the same feelings.

In fact for most people the experiences are qualitatively different with no initial 'rush' following consumption and a reduced euphoric effect. A larger dose of methadone only makes people feel like they have had more methadone - it does not make them feel like they have taken heroin.

Methadone has a slow onset of action
The physiology of this phenomenon is described in Section 4. This causes two problems. Firstly people who have taken illicit methadone on an occasional basis may believe that they need a larger dose than they really do in order to achieve absence of withdrawal symptoms. Secondly, clients get maximum effect from the methadone about 72 hours into treatment when they usually want maximum effect within a few hours.

These problems can be largely resolved, and clients helped to accept a realistic therapeutic dose, by giving an understanding of the issues, and by clinicians acknowledging the psychological pressures which exist for clients who are making the transition from heroin to methadone.

The dangers of prescribing too much/not enough

Accidental overdose
Accidental overdose is one of the greatest risks of methadone prescribing.

Patients who cannot be observed for at least 4 hours following administration of the first dose of methadone should not be allowed to take a dose greater than the minimum lethal dose of 50mg. If there is any risk of the use of alcohol or other depressants prescribers must bear in mind that the lethal dose will be lower still.

Illicit sales
A certain amount of illicit selling of methadone is an unavoidable consequence of any methadone prescribing programme that allows clients unsupervised methadone consumption. It is commonly referred to as 'spillage' or 'leakage'.

Sale of the initial doses will occur only if the initial assessment has seriously over estimated the amount of methadone required and/or the client's intentions to switch to methadone treatment.

At the start of methadone treatment leakage to the illicit market is less likely and can be minimised by careful prescribing and monitoring of the client in the early stages of their treatment.

Not prescribing enough
Opiate users presenting for methadone treatment will have a clear expectation that methadone will 'hold' them and prevent them experiencing withdrawals. Education about what to expect over the first few days of treatment (see above) cannot compensate for an inadequate dose, the result of which is likely to be continued illicit drug use and/or dropping out of treatment.

How much methadone should you prescribe?
If you have decided to prescribe methadone and have reached a conclusion about:

• The amount of opiates you believe the client to be using
• The treatment aims

you then need to make a calculation as to the appropriate therapeutic dose.

If the client is using prescribed pharmaceutical opiates then the conversion is fairly easy. However this is rarely the case. With illicit drug users assessment of actual drug use is discussed at length in the suceeding section.

For non-specialist prescribers the essential rules to remember are:

• Start on a safe, low dose and work up
• The lethal dose for a non-tolerant adult is around 50mg
• If in doubt refer to a specialist drug service and/or prolong the assessment period.

Non-specialist prescribers should not prescribe collected doses of more than 50mg until tolerance has been established.

Where the starting dose is pitched the range of equivalent doses will depend on factors such as:

• The amount of control the person has over their drug use
• The level of motivation to stop using illicit opiates
• Whether or not they inject
• How soon it is planned to reduce the methadone dose
• The risk of overdose
• Anticipated concurrent alcohol/other depressant drug consumption.

It is always important to bear in mind that it is easier to increase the dose after the first week of treatment if it is proving insufficient than to reduce it if you think it is too much and the client disagrees!

Methadone equivalent doses
It is not possible to directly convert the effects, duration and dependence potential of other opiates to a fixed equivalent in methadone. Therefore these charts must be used with caution and in conjunction with the explanatory text above.

Pharmaceutical opiates

Illicit heroin to methadone conversion
Conversion of illicit heroin consumption into an appropriate methadone dose is complicated by all the factors outlined above and in Section 6: Assessment. It varies widely according to local practice.

This table is a guide only and should not be used without consultation with your local drugs service.

There is room on the table for you to add the optimum dose for your service. It is filled in here with approximate values which give a typical range for the figures.

Illicit heroin conversion chart

Please note: the maximum initial dose is 40mg, the doses below are an indication of where you might expect people to stabilise as you increase dose during the first 1-3 weeks of treatment.

Ounces to grams conversion
Heroin is bulk bought in fractions of an ounce, if a client is referring to their consumption in ounces use the conversion chart below to convert back to grams.

Ounces to grams conversion chart

Dose titration
The aim is to titrate the methadone dose against any signs of withdrawal and cravings for or actual illicit opiate use, during the first three days of treatment. The client should be seen regularly to assess whether any withdrawal signs are present. If these are observed the daily dosage can be increased by up to 10-20%. By the third day the total daily dose should provide a reasonable baseline for either a reduction or longer-term prescribing.

Administration of the initial dose
This can be given either as a single dose or divided into 2 doses 12 hours apart. Either way it is preferable to observe the client for at least 2 hours after the first dose to ensure they do not become intoxicated and so reduce the risk of overdose. If there are signs of intoxication the observation period should be extended to 4 hours and consideration should be given to reducing the dose.

As it is not always possible to estimate accurately the equivalent dose of street heroin some practitioners (usually those with access to in-patient facilities) start with a dose of 20mg methadone and observe. If withdrawal signs remain 2-4 hours after this dose a further 20 mg is given and so on, up to a usual maximum of 50 mg in the first 24 hours. The first day's total dose is the starting point for day 2 and any further increases are titrated against withdrawal signs.

Opiate users - particularly those who have been using high doses of illicit methadone - may have a very high tolerance and be able to take doses in excess of 100mg without appearing intoxicated. Dose titration should therefore be against cessation of withdrawal symptoms rather than indications of intoxication. Also remember that people who have had a break from regular opiate use, perhaps through detox or a prison sentence, and are asking for methadone in the early stages of relapse to illicit heroin use may have a much lower tolerance for methadone than they think.